Control means for highway crossing signals



Aug. 18, 1936. N. D. PRESTON 2,051,418

CONTROL MEANS FOR HIGHWAY CROSSING SIGNALS Filed Dec. 19, 1930 4 Sheets-Sheet 1 1936. N. D. PRESTON CONTROL MEANS FOR HIGHWAY CROSSING SIGNALS Filed Dec. 19, 1950 4 Sheets-Sheet 2 1.? .5 J J E hj Aug. 18, 1936. N. D. PRESTON CONTROL MEANS FOR HIGHWAY CROSSING SIGNALS Filed Dec. 19, 1930 4 SheetsSh ;et 3

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CONTROL MEANS FOR HIGHWAY CROSSING SIGNALS Filed Dec. 19, 1930 4 Sheets-Sheet 4 I) m k) J n 1 E INVENTOR Patented Aug. 18, 1936 v UNITED STATES PATENT OFFICE CONTROL MEANS FOR HIGHWAY CROSSING SIGNALS Neil D. Preston, Rochester, N. Y., assignor to General Railway Signal (iompany, Rochester,

4 Claims.

This invention relates to signalling systems particularly adapted for protecting vehicle traffic on highway crossings over railroads, and more particularly to the control of a highway crossing signal of any suitable type.

In accordance with this invention, it is proposed to provide means, governed by trains approaching a highway crossing, which will act to actuate the highway crossing signal at a substantially fixed and uniform time interval before the arrival of the train at the crossing, ir respective of the speed of the approaching train.

Other characteristic features, objects, and advantages of the invention will be in part apparent, and in part pointed out, as the description progresses.

In the accompanying drawings, Fig. 1 illustrates in a simplified and diagrammatic manner one embodiment of the invention, the various parts being shown more with the object of making it easy to understand the nature of the invention, than to show the detail construction and arrangement of parts preferably employed in practice;

Fig. 2 shows how the invention may be applied to a single track railroad, or other stretches of track, where trains approach the highway crossing from both directions; and Fig. 3 shows a modified embodiment of the invention, in which provision is made for discontinuing the warning indication of a highway crossing signal after it has been given longer than a predetermined time. Fig. 4 shows a modified form of the invention, in a wholly diagrammatic manner.

Referring to Fig. 1, H designates a highway crossing a railroad at grade, and G designates an electrically controllable highway crossing signal of any suitable type, which may be any one of the well-known types of bells, wigwag signals, flashing light signals, and even poweroperated gates. The railroad track on one side of the crossing, dependent upon the normal direction of train movements, is provided with two insulated track circuit sections T--I and T-Z, having track relays IT and 2T. The track circuit section T-2 extends from the crossing to a predetermined point B distant from the crossing; and the track section T--I extends from the point B to a point A farther away from the crossing. The length of the track circuit section T-2 and the proportional length of the other track circuit section T-I are selected in accordance with the principles hereinafter explained.

The highway crossing signal G (indicated conventionally as a bell) is controlled by the track relays IT and 2T, and also by a timing mechanism, which in the simplified arrangement shown comprises a cam 5, co-operating with a roller 6 5 to open and close pairs of spring contacts 1 and 8.

The contacts I and 8 are biased to the open position by their own spring pressure, or if desired an extra spring may be provided to urge 10 the roller 6 toward the cam 5. The cam 5 is fixed to a shaft 9, indicated by dotted lines, and a pinion ID on this shaft operates a pivoted weighted sector I I, having its lower position fixed by an adjustable stop screw I2. Also fixed to 15 the shaft 9 is a gear I3, having a mutilated portion I4, which forms part of a reduction gearing of any suitable type, including gears I5, l6, and I1. The gear I! is fixed to a shaft I8, which is connected to the armature of an electric motor 20 M of any suitable type having constant speed characteristics. Also fixed to the shaft I8 is a ratchet wheel I9 engaging a spring pawl 20 carried by a gear 21 loose on the shaft I8. This gear 2| drives a pinion 22 which is connected to; 5

a shaft 23 supporting and operating a centrifugal brake and circuit controlling device. CB. As diagrammatically shown, this centrifugal device CB is of the usual fiy-ball governor type, which raises an insulated contact disc 24 out of en- 0 gagement with stationary contacts (indicated as arrows), and into engagement with stationary brake members 25.

The arrangement shown in Fig. 1 also preferably includes special control of a wayside automatic block signal governing train movement toward the crossing. This/signal S, shown conventionally'as a semaphore signal, is located at the entrance end of the track section T-I, and is assumed to be controlled by a line relay I-ID, in accordance with recognized practice. The energizing circuit of this line relay HD includes a front contact 30 of the track relay IT, contacts I of the timing mechanism, and various other controlling contacts (designated conventionally at 3|) which are necessary to provide the desired control of the signal S.

Other features of construction and characteristic features of this invention will be made clear upon considering the mode of operation.

When the head-end of a train approaching the crossing passes the point A and enters the track section TI, the track relay IT is shunted, and the motor M is energized over a circuit which may be traced from (designating one tergized in multiple'with the motor.

minal of a suitable source of operating current),

' through front contact 32 of the track relay 2T,

wire 33, back contact 34 of track relay IT, wires and 36, and motor M to (indicating the opposite terminal of said source of current). At the same time, the slow-release relay SL is enerbeing thus supplied with current, drives the shaf t I3 at auniform'rate in a counter-clockwise direction, causing the pawl 20 to click idly over the ratchet wheel 19. Also the shaft I8 through the reduction gearing drives the shaftS in a counter--' clockwise direction, indicated by the arrow a,

raising the weightedsector N;

This operation, conveniently considered as a winding-up operation, continues until the head 'end of theapproaching train passes the point B and enters the track section T -2, whereupon' the track relay 2T is shunted, the energizing circuit forth'e motor M is broken at" its front contact 32, and the motor M is de-energized. The motor M being de energized, the weighted Sector II drives the shaft Bin the opposite or clockwise direction, indicated by the arrow b. Likewise the shaft I8 is driven in the same direction, rotatingthe gears 2| and 22, and the centrifugal brake CB, through the ratchet wheel i9 and pawl 20. 'This centrifugal brake CB retards this run-down movmentof the shaft 9 and cam 5 to a predetermined, rate, and after a 38 and 39, signal G, to 7 1 The operation of the system embodying this invention; thus briefly described, involves a number of factors of speed, time, and distance, ,which determine the'lengths of the track sections Tl andv T -ZJand the design and proportion of p'artsrof the timing mechanism, so

as 'to obtain the result desired. Analyzing" the principles. governing the operation'of the invention, it will be noted that the energizing circuit for; the signal G, which is closed to cause this signal to give its warning of an approaching train, includes in series .the back contact '32 of the track relay 2T and the contacts 8 ofthe. timing mechanism. This back contact 32ris closed when the approaching train passesithe point B and'shuntsth'e track relay 2T; 'but the signal is not actuated until the contacts 8 of the timing mechanism arealso closed. These contacts 8 of the timingmechanism areopened during the wind-up operation (rotation of shaft ,9 in direction indicated. by arrow 'a), which 2 takes place while the approaching train is passing over the distance between the ,points A and BI V -Itshould be noted the contacts 8 are closed by'the cam 5 in its initial run-down position,

' and remain closed during the angular movement of the cam designated 3:. Consequently, during the wind-up operation of the timing mechanism the contacts 8 remain closed, until thelcam 5 has j been rotated counter-clockwise through the angular'distan'ce .73, far enough for the roller 6 to rideofi of the end of the cam surface; whereas, during. the run-down operation of the timing mechanism. (rotation of shaft 9 indirection indicated-by arrow b), the contacts 8 are closed as soon as the cam reaches an intermediate 7 pointfcorrespohding to the angular distance a:

7 from its initial run-down position. In short, the 75 7 time interval represented by the angular dis- The motor M,

proaching train actually reaches the crossing.

screw l2.. It will be evident that adjustment of .ally shorter than the track section T 2; Stated? tance x, for a given rate of rotation of the shaft 9, is a part of the wind-up time, but is subtracted from the run-down time. This interval of time, corresponding to the angular distance a: V of rotation of the cam 5 at a given rate, repre 5 sents the time considered necessary and safefor vehicles approaching or passing the railroad to come to a stop or clear the crossing, after the signal G has been actuated, and before the, ap-

This time interval, which may be considered to "be the safe clearing time for the railroad crossing, may be varied by adjusting the initial rundown position of the cam 5 by means of the the screw 12 up or down will lengthen or shorten the angular distance '32.

The track section'T--2 is made at least as long as, and preferably longer than, the distance' over which a train running at maximum speed will travel during the clearing'time selected as safe for actuating the signal G before this high'speed train actually reaches the crossing. In other words, the length of the track section T2 is such, that. if the signal ,G is 'actu-c25 ated to give the warning of an approaching a train, running at maximum speed, enters the track -section'T2, a safe clearing time for vehicles to stop or' clear the crossing willelapse before this high speed train actually arrives at the crossing.

7 Having thus determined the length ofnthe 7 the ratio of the rate of wind-up movement of the cam 5 to the rateof its run-down movement. For example, if thecentrifugal brake device CB 'is' designedand-adjusted to regulate the rate of the return movement of the shaft 9 in the clockwise direction (indicated by arrow 12) to the same rate at which this shaft isrotated in the counter-clockwise direction by the motor M, then the track sections T-| and T'2'are made substantially the same length. If, however, the rate of the run-down movement is made slower than that of the wind-up, as can be; readily accomplished by proper proportioning of the parts, then the track se'ctionT-J is made proportionanother way, with given rates of rotation of the shaft 9 and cam 5 for wind-up and run-down .moveme'nts, determined by the design and'proportioning of the parts of the timing mechanism, the relative lengths of the track section; T-I and T2' are selected in the installation of the invention, so as to cause the cam 5 to rotate through the same angular distance during the movement of a train travelling at uniform speed through thesetrack sections.

Bearing in. mind'these factors of time and distance which-determine the proportioning of the parts for an installation of this invention,

it'will'be observed that the timing mechanism is wound up during the time taken by the ap- 'proaching train to travel the distance between the points 'A and B, corresponding 'to the length of the track section T the'operation of the timing mechanism being initiated by the shunt- .ing of the track relay IT to close its backcontact 34, and being terminated by the shunting of the track relay 2T to open its. front contact "32'. Thus, the angular movement of the cam 5 W from its initial run-down position taking place during the wind-up operation of the timing175 mechanism varies with the speed of the approaching train. The higher the speed of this train, the shorter the time interval of the winding operation, and the smaller the angular movement of the cam 5.

When the approaching train passes the point B, the run-down operation of the timing mechanism starts, and after a time interval which depends upon how far cam was rotated during the wind-up operation, the contacts 8 are closed to actuate the signal G. With a train running at the maximum speed, the cam 5 is moved during the wind-up operation to a point only a short distance beyond the point where the contacts 8 are closed, so that these contacts 8 are quickly closed after the train enters the track section T2 and the run-down operation starts. In other words, for a train running at maximum speed, the signal G is actuated at about the time this train passes the point B. If the length of the track section T-2, from the point B to the crossing, is such that this maximum speed train will reach the crossing at the selected clearing time, represented by the angular distance :r, then the contacts 8 close promptly upon shunting of the track relay 2T; but with a longer track section T2, the cam 5 may be moved during the wind-up operation farther than the angular distance x and the closing of the contacts 8 is delayed for a corresponding time interval.

In the case of a slow-speed train approaching the crossing, the cam 5 is rotated counter-clockwise much further than the angular distance 3:, dependent upon the speed of the train and the time taken by it to travel through the track section T-I; and it will be evident that there is a corresponding delay in the closing of the contacts 8 after this train enters the track section T--2, so that the actuation of the signal G is delayed until such slow-speed train has reached a point where the time required for this train at the same speed to reach the crossing is the selected safe clearing time, represented by the angular distance :13.

In this way this invention provides means which causes actuation of a highway crossing signal to give warning of an approaching train at substantially a fixed and uniform time before such train actually reaches the crossing, regardless of the speed of this approaching train. Without the special control of a highway crossing signal in accordance with this invention, it will be evident that the signal must be given at a fixed point, located a predetermined distance from the crossing and far enough away to actuate the signal in time for the highest speed approaching train, with the result that the signal is given long before a slow train actually reaches the crossing. With such a control of a highway crossing signal on the fixed distance interval basis, the operators of vehicles obeying the signal frequently have to wait at the crossing for a slow train so long that they lose confidence in the signal; and after some unnecessary long waits at crossings, when strictly obeying the indication of the signal, the operators of vehicles frequently disregard the signal, thinking that there is plenty of time to cross the railroad before the train arrives, this being done sometimes even though the approaching train can be seen. It is very difiicult, however, to judge the speed of an approaching train, particularly at night; and accidents have occurred where the operator of the vehicle, having become accustomed to disregard the indications of the highway crossing signal-and to rely on his own judgment of the time of arrival of the approaching train, makes: an.

the signal G and the actual arrival of the train,

will of course be exactly the same for different speed trains, within the limits of accuracy of the timing mechanism, only if each train maintains a uniform speed between the point A and the crossing. If the approaching train materially changes its speed in this distance, this clearing time will be somewhat shorter or longer. A railroad train, however, cannot quickly change its speed, and a clearing time can readily be selected to provide the desired safety, without producing unnecessary delay, in spite of such variations of train speed encountered in practice. On account of such speed variations, it is preferred to make the track section T-l relatively short, so that the wind-up movement of the cam 5 is a substantially accurate measure of the actual running speed of the train. For example, if the track section T-l were made as short as 200 feet, it is evident a railroad train could not materially alter its speed in travelling such a short? distance, either in accelerating or in braking. If a train should slow down after passing the point B, then the signal G is actuated sooner than necessary to provide the selected clearing time;

and if the train should accelerate after passing the-point B, the clearing time is shortened. These variations can be taken care of for all practical purposes by selecting the proper clearing time interval.

In order that the timing mechanism may not.-

be damaged in case a train should happen for any reason to stop in the approach timing track section Tl, the gear 13 is provided with a mutilated portion l4, so positioned that when this gear l3 and the shaft 9 have been rotated to the extreme woundup position, the gear I5 turns idly in this mutilated portion. If desired, a suitable friction clutch may be interposed between the motor and the shaft H! for the same purpose.

In sucha system of signalling for highway crossings, it is important that all probable failures of the mechanism and circuits should, as far as practicable, be on the side of safety. In the embodiment of the invention shown, if the timing mechanism should for any reason fail to wind up, the contacts 8 remain closed, and

the signal G is actuated as soon as the approaching train enters the track section T2. If the timing mechanism, having been Wound up to a position to open the contacts 8, should for any reason stick in that position and fail to return and close these contacts, the signal G would not be properly actuated; and to protect against this contingency, an auxiliary cir-;

cuit for displaying the signal G is provided from back contact 32 of track 2T, wires 31 and 40, back contact 4! of relay SL, wire 42, contacts 24 of the centrifugal brake device CB, wires 43 and 39, signal G, to

If the timing mecha' anism, after having been wound up, should fail ,to return, the centrifugal device GB is not rotated andits contacts 24 remain closed. Consequently, when the approaching train enters the. track, section T -2 andbreaks the, encrgizing circuit for the'relay SL at the front contact .32 of the trackrelay 2T, the back contact highway crossing system.

actuated, even though the contacts 8 may be open. The'relay SL is made sufficiently slow releasing, by the, use of copper slugs or any one of the various well-known expedients, so that upon simultaneous de-energization of this relay and the motor M, there will be suflicient time for the weighted sector H to start the rundown movement and'open the contacts .24 of the centrifugal brake device CB before the back contact 4| of the relay SL is closed.

As a'further check upon the performance of the timing mechanism of' this invention, if .desired, the wayside block signal S, governing traffic toward'the siding, maybe controlled by the contact! as shown, so that if the contact 8, which is mechanically connected to and operated concurrently with the contactl, is open for any reason, the block signal S is held at stop, thus manifesting a defect in the operation, of the It is contemplated that the engineers of passing trains, finding the block signal S at stop, when there is no train ahead, will report the matter, sothat the failure of the timing mechanism will be quickly discovered and remedied. r

'In the arrangement shown in Fig. 1, it is assumed that trains always approach the crossing in one direction; and'Fig. 2 illustrates how the p principles of the'invention may be applied to a single track railroad, or other track location, where trains may approach the crossing from either direction.

In making such an application of the invention, any one of the well-known types of interlocking or stick'relay circuits 'now commonly employed for controlling highway crossing signals, may be used to control the timing mechanism of this invention. In the arrangement shownin Fig. 2, two track sections, corresponding to thetrack sections T--I and T2 of Fig. 1, are provided on each side side of the highway crossing; and the track relays IT and 2T,

and ST and 4T, of these track sections controli V the energization of thetwo coils RE and RW of an interlocking relay of the usual type, such as, disclosed for example inthe patent to T. L.

Lee, No. 885,061, dated April 21, 1908. When both of thecoils RE and 'RW of such an interlocking relay are energized, then upon de-energiz ation of either coil, the armature of that deenergized coil may drop down and close its back contact, and lock up the armature of the other coil. j Y

Considering the operation of this. arrange- .ment shown in Fig. 2, assume that an east bound train, travelling from left to right, enters the track section T|. The opening of the front contact of the track relay'lT de-ener- I gizes the coil RE of the interlocking relay, clos- Y ing its back contact 46 and establishing an energizing circuit for the motor M'from back contact 46, wire 41, front contact of relay 2T, Wires 49 and 50, motor M to When this approaching train enters the track'section T-Z, the opening of the front contact 48 of the track relay 2T breaks the energizing circuit for the motor M of the timing mechanism; and the pass. the crossing for some time.

this invention contemplates the provision of" closing of the back contact 48 of this relay 2T establishes a circuit for actuating the signal G from back contact 46 of coil RE of the interlocking relay, wire 41, back contact 48 of track relay 2T, wires 5| and 52, contacts 8 of 5 the timing mechanism, wire'53 and'signal G to When this train passes the crossing H. and enters the track section T-3, the dropping of the track relay 3T de-energizes the coil RW of the interlocking relay, but since the coil RE 10 was first de-energized the armature ofthe coil RWislocked up, and remains so until the train in question has passed out of the track section T-4. When the rear end of the train passes the crossing H and enters the track section I -3,115

The operation is the same for a west-bound'g2 0 train travelling in the opposite direction; and it can be readily seen that the signal G is actuated to give warning of a train approaching the crossing from eitherdirection, with the same control by the timing mechanism as previously err- 25 plained in connection with Fig. 1.

. Highway crossings are sometimes located at such places. along a railroad that trains occasionally come to a stop and waitfor a long time, or. switch back and forth, near the cross-.;-

ing within the control limits for the highway crossing signal. For example, a'turn-o'ut switch SW may be located, as shown in Fig. 3, in or close to the track section T- 2 adjacent the crossing, so that this track section 'I2 may: i .5

be occupied for a long time by a-train switching cars over this switch SW. In cases of this kind, the highway crossing signal G maybe actuated to display its warning indication and block the crossing, for a long time; and it is 40 desirable to. provide means for discontinuing this warning indication, notwithstanding the presence .of a train adjacent the crossing, when such train is standing still, or will not actually means, such as shown in Fig. 3, for cutting off or suppressing the warning indication of the signal G after a time interval. In this connection, it should be understood that, when a train, 50

for any reason, after entering the track section T2, is delayed for a considerable time before passing over the crossing, its movement over the crossing will be made at a slow speed and with suitable hand signal protection for the vehicles on the highway. 7

Referring to the modification shown in Fig.

7 3, a'thermal time element device TE and a stick relay S, with suitable control circuits, are proe vided to shunt or short-circuit the signal G after this signal G'has been actuated for a predetermined time by a train on the track section T-2. The thermal time element deviceTE is of the type shown and'described', for example, in the application of ,J. E. Willing, Ser. No."463,903,-

filedJune 26, 1930, and comprising a bi-metal- 110 member 55, surrounded by a heating coil 56. V

. Whenthe heating coil 56 is supplied with cur.-

rent, the'member 55. is heated and is bent or displaced from its normal cold position, this displacement being gradual and substantially in accordance with the lapse of time. The member 55 engages contacts indicated by arrows in its normal cold position, and in its heated position. In this modified arrangement shown in Fig. 3,

Accordingly 45 when the signal G is actuated, as previously explained, by the closing of the contacts 8 of the timing mechanism and the back contact 32 of the track relay 2T, another pair of spring contacts 51, mechanically connected to the contacts 8, are also closed, and another back contact 58 of the track relay TI is likewise closed, thereby establishing a circuit for supplying current to the heating coil 55 of the time element device TE from through the back contact 59 of the stick relay S, wire 60, heating coil 55 connected to the member 55, wire 59, contacts 51, wire 62, back contact 58 of track relay 2T to After a predetermined time, dependent upon the design and proportioning of the parts of the thermal element and the intensity of its heating current, the member 55 is bent or displaced far enough to close its normally open contact, whereupon a pick-up circuit for the stick relay S is established from relay S, wires 63 and 6 member 55 in its heated position, wire 6| contact 5'!, wire 62, back contact 58 of the track relay 2T to Upon energiza tion of the stick relay S, it is maintained energized by a stick circuit through its own front contact 59 and the contacts 5? and 58, in series with .the heating coil 56. The resistance of the relay S is such as to reduce the current through the heating coil 56 to such a small amount that the thermal member 55 gradually cools off; and when this member 55 returns to its normal cooled position, after a further lapse of time, a partial circuit for shunting out the signal G and causing it to assume its inactive condition is established, from wire 39, over wire 65, suitable limiting resistance 66, wire 6?, front contact 68 of relay S, wire 69, member 55 in its cooled off position, wire 6!, contacts 5'5, wire 62, and back contact 58 of track relay 2T to Thus, after a predetermined time interval, necessary for the thermal member 55 to become heated and then again cooled, the highway crossing signal G is cut out or suppressed. When the train on the track section T2, causing actuation of the signal G, leaves this track section, and the back contact 58 of the track relay 2T is opened, the stick relay S is de-energized, and the parts are restored to the normal condition, ready for the next operation.

In some types of highway crossing signals, particularly the type commonly known as wigwag signals, the signalling device is actuated to display its warning indication by opening a normal closed and energized circuit, rather than closing a circuit; and Fig. 4 illustrates how the control circuits for a signal of this type can be organized in accordance with this invention.

Referring to Fig. 4, the signal G is assumed to be controlled by a normally energized control relay GR and to be actuated when this relay is de-energized. The control relay GR is normally energized over a circuit from front contact 10 of the track relay 2T, wires H and I2, relay GR to When the approaching train enters the track section T2, the opening of this front contact "at of the track relay 2T breaks this circuit for normally energizing the relay GR, and unless an auxiliary energizing circuit for said relay is established, the signal G is actuated.

In this modified arrangement shown in Fig. 4, the cam 5 is shaped to close normally open contacts 8 after this cam has been displaced from its normal run-down position hrough the angular distance as. The timing mechanism is wound up during the movement of the approaching train through the track section T-!, and when this train enters the track section T2, the opening of the front contact 32 of the track relay 2T de-energizes the motor M and the relay SL, in the same way as previously described. The control relay GR is maintained energized under these conditions by a circuit from contacts 5.3 wires 73 and M, front contact E5 of relay SL, wires it, 5?, and relay GR to When the timing mechanism begins its rundown movement, the contacts 24 of the centrifugal device CB close before the front contact E5 of the relay SL opens, and the control relay GR. is maintained energized until the cam-operating contact 8 opens. If the timing mechanism should fail to start and close the normally open contacts 8 or should fail to iun down and close the contacts 24 of the centrifugal brake device CB, the relay GR is deenergized upon opening of the front contact iii of the track relay 2T, thereby actuating the signal G, in spite of such failures.

The embodiments of the invention shown and described are merely illustrative or typical of the ways in which the principles of the invention may be practiced; and various additions, modifications, and adaptations may be made in the particular construction and arrangement of parts and circuits shown and described, without departing from the invention. It should be understood that any type of highway crossing signal may be actuated in accordance with this invention; that any desired source of current may be employed for the energization of this signal and its control devices and circuits; and that train actuated track instrument devices may be used instead of the track circuits.

What I claim is:

1. In a signalling system for highway crossings on railroads, the combination with a signal at the crossing, a timing mechanism wound up from an initial position at a predetermined rate during the time taken by an approaching train to travel a predetermined distance remote from the crossing, said timing mechanism automatically returning to said initial position at a predetermined rate and actuating circuit controlling means at a time interval prior to reaching said initial position, contacts closed only when said timing mechanism is returning to its initial condition, and a circuit governed by said circuit controlling means and said contacts for controlling said signal.

2. In combination, a stretch of railway track intersected by a highway, a crossing signal located at the intersection, means for setting the signal into operation when a train approaching the intersection reaches a fixed point, a time measuring device comprising a member biased to an initial position and a prime mover moving it away from such position, means for energizing said prime mover before a train reaches said fixed point and for de-energizing it when the train reaches such fixed point, means including said measuring device for delaying the operation of said signal, and means for cutting said delaying means out of service if said member stops even temporarily during the portion, necessary for signal initiation, of its return movement.

3. In combination, a stretch of railway track intersected by a highway, a crossing signal lo-- cated at the intersection, means for setting the signal into operation when a train approaching an initial position and aprime'mover moving it away from such position, means for energizing asaid' prime mover before a train reaches said fixed point, means including said measuring device for delaying the operation of said signal,

and means for at once cutting said delaying means out of service if said member stops during a predetermined portion of its return movement. 7 V

4. In combination, a stretch of railway track intersected by a highway, a crossing signal 10- cated at the intersection, means for setting the signal into operation when a-train approachingj the intersection reaches a fixed point, a time measuring device comprising a memberbiased' to an initial position and a prime mover moving it away fromsuch position, means for energizing said prime mover before a train reaches saidfixed point, 'means including said measuring device for delaying the operation of said signal,

and means'for cutting said delaying means out 10 of service if and when said member stops during its return movement. v s NEIL D. PRESTON. 

